Tab count should somehow reflect the number of both source-level annotations and replies

Let ```x``` be the number of top-level annotations in a tab.
Let ```y``` be the total number of replies for the top level-annotations in this tab.
Let ```z``` be the total number of annotations (top+reply) in this tab. ```z```  = ```x``` + ```y```

Originally, we had been displaying: ```z```
After the first iteration we were displaying: ```x```

Now the displayed label is constructed following the rules below:
- If there are no replies we display: ```x``` (which is in this case equals to ```z```)
- If the sum of digits of ```x``` plus ```y``` + 1 (the plus sign) is smaller than 5 we display: ```x+y```
- otherwise we display: ```z```

Will solve #671